The invention relates to a brake booster according to the preamble of claim 1. Such a brake booster is known from DE 44 22 027 A1.
Such a brake booster is frequently implemented as a vacuum brake booster and has a housing which is divided by a movable wall into a vacuum chamber which is continuously connected to a vacuum source, and a working chamber which is adapted to be selectively connected to vacuum or to at least atmospheric pressure. The connection of the working chamber to vacuum or to at least atmospheric pressure is provided by means of a control valve which is located at the brake booster and can be actuated electromagnetically either by means of the force of the driver's foot which is exerted via, for example, a brake pedal, or by means of an electromagnetic actuation which is independent of the force of the foot.
The components of the electromagnetic actuation, in particular the solenoid coil, the coil housing, the magnet armature and an armature counter-element, when the system is excited, form a magnetic circuit which acts on the magnet armature and generates a desired lifting force there in order to lift off the first valve seat of the control valve from the rubber-elastic sealing element. The magnetic circuit extends from the coil via the coil housing to the magnet armature and from there via the armature counter-element back again to the coil housing. A specific material cross section or, in other words, a specific, definable quantity of magnetic or magnetizable material is necessary in this magnetic circuit to achieve an optimum magnetic flux. If the magnetic circuit contains more than this specific quantity of magnetic or magnetizable material, the resulting gain in magnetic flux will only be small.